Method for electrolytically forming a coating of titanium-alkaline earth metal compound oxide

ABSTRACT

A METHOD FOR FORMING A COATING OF TITANIUM-ALKALINE EARTH METAL COMPOUND OXIDE ON THE SURFACE OF TITANIUM USED AS ONE OF THE ELECTRODES IN AN ELECTROLYSIS, IN WHICH SAID ELECTROLYSIS IS CARRIED OUT IN A BATH CONTAINING HYDROXIDES OR SALTS OF ALKALINE EARTH METALS AND EMPLOYING ALTERNATING CURRENT POWER SOURCE.

Aug. 7, 1973 HIRQSH] NQZAKI ETAL 3,751,349

METHOD FOR ELECTROLYTICALLY FORMING A COATING OF TITANIUM-ALKALINE EARTH METAL COMPOUND OXIDE Filed March 24, 1971 30 l I 1 I I l Time(min) United States Patent 3,751,349 METHOD FOR ELECTROLYTICALLY FORMING A COATING OF TITANIUM-ALKALINE EARTH METAL COMPOUND OXIDE Hiroshi Nozaki, Chiba, and Masaki Yamazaki, Ueda, Japan, assignors to Stanley Electric Co., Ltd., Tokyo,

Filed Mar. 24, 1971, Ser. No. 127,648 Claims priority, application Japan, Mar. 27, 1970, 45/ 25,270 Int. Cl. C23b 11/02 US. Cl. 204-56 R 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method for forming a coating on the surface of titanium.

More particularly, this invention relates to a method for forming a coating of titanium-alkaline earth metal compound oxide on the surface of metallic titanium.

There has never been known in the ordinary art that a layer of titanium oxide containing alkaline earth metal is formed by oxidizing the surface of titanium by means of alternating current electrolysis.

Titanium oxide has several characteristic properties such as high dielectric constant, and high responses to temperature in respect of the electric resistance and electrostatic capacitance, accordingly if it is possible to obtain a stable and durable coating made of titanium-alkaline earth metal compound oxide on the surface of titanium, various uses will be expected. In this respect, the inventors have carried out extensive experiments in order to obtain satisfactory coating on the surface of titanium, and as the result, the inventors have found the method for forming said coating film on the surface of titanium, the method of which will be described in the following.

In the method of the present invention, an aqueous solution of hydroxides or salts of alkaline earth metals is employed as electrolytic bath, and any metallic titanium material is employed as one electrode for the electrolysis by using alternating current. Said compound oxide coating containing alkaline earth metal can be formed by oxidizing the surface of titanium by means of alternating current electrolysis using said aqueous solution and said titanium electrode.

In the method of the invention, the surface of titanium may be preferably treated with alternating current electrolysis in a dilute sulfuric acid solution bath in advance of the aforementioned electrolysis in the solution of hydroxides or salts of alkaline earth metals, by which more preferable coating can be obtained.

Thus obtained compound oxide in accordance with the method of the present invention, contains oxides of alkaline earth metals which have been used for the electrolytic bath, and the compound oxide has various characteristics and utilities as disclosed in the following.

(A) A small sized electrostatic capacitor with large capacitance can be made by using said oxide coating on the surface of titanium.

(B) As it shows high response to temperature in the electric conductivity and electrostatic capacity thereof, several elements for electronic circuits can be made utilizing these characteristics. Transient phenomena of electric conductivity and dielectric constant are observed with 3,751,349 Patented Aug. 7, 1973 the change of temperature, therefore utilizing this characteristic, a circuit which shows response only to the rapid change of temperature and does not to the gradual change of temperature, can be made. For example, such circuit that shows response to the change of temperature in the range of 10 C. per 3 minutes and does not show response to the same change per 20 minutes, may be manufactured. Or such circuit that the switch is turned off in response to the rapid change of the temperature and the switch is turned on again as the temperature returns to the original value, can be made.

(C) Oxide of titanium has anticorrosive property, therefore it can be used for anticorrosive containers, machine parts and accessories.

As mentioned in the above, the metallic titanium having the coating formed in accordance with the method of the invention has various utilities, which can be obtained only by the method of the present invention.

The method of the present invention will be explained in further detail in the following.

For example, the preliminary electrolysis is carried out in a dilute aqueous sulfuric acid solution with the concentration of from 10 to 20% by weight, in which a metallic titanium plate is used as an electrode, a platinum or a graphite electrode is used as another electrode, 50 cycles alternating current is used as electric source, and the electrolysis is carried out for 1 to 3 hours under the current density of 50 to ma./cm. as for said titanium plate-.- Thereafter, the titanium plate is rinsed with pure water. Without saying, this preliminary electrolysis step is taken effect in order to improve the formation of the coating, and it can be omitted without serious disadvantages.

In the next step, the main electrolysis is carried out in a bath consisting of, for example, saturated solution of barium hydroxide [Ba(O'H) -8H O], in which the aforementioned pretreated or not pretreated titanium plate is used as one electrode, a platinum or a graphite plate is used as another electrode, 50 cycles alternating current is employed as the electric source, and the electrolysis is carried out for 30 minutes to 2 hours under the current density of 50 to 100 ma./cm, then for 30 minutes to 2 hours under the current density of 75 to Ina/cm. and further it is continued for 1 hour to 3 hours under the current density of 100 to ma./cm. thus the surface oxidation can be effected. On this occasion, the temperature of the electrolytic bath may be made between 20 to 70 C., and the aforementioned saturated solution of barium hydroxide is those saturated at the respective temperatures. By the way, 100 g. of the saturated solution contains 3 g. of barium as barium oxide (BaO) at 20 C. and 10 g. at 50 C.

Through the above steps, the titanium plate is then rinsed with pure water to obtain a titanium plate coated with titanium-alkaline earth metal compound oxide of the present invention.

The compound oxide thus obtained is a stiff and polycrystalline film in the thickness of from 2 to 3 microns, and it contains barium. With regard to this oxide, the dielectric constant and electric conductivity thereof show transient phenomena by a rapid change of the temperature.

Through the above-described method, titanium which is coated with compound oxide of the invention can be obtained, and this has never been realized in the prior art. Owing to the characteristic features of the high dielectric constant and the transient phenomena of the compound oxide, the following uses are expected.

(a) Uses for the devices to prevent or check the changes of temperatures such as a thermostat or a fire alarm.

(b) Uses for switches of the circuit or the like which generates heat by utilizing the characteristic of the large response to the rapid change of temperature.

(c) Uses for compensation of temperature, for example, for condensers in electronic circuits by utilizing the response of dielectric constant of the oxide film to the rapid change of temperature.

(d) Uses for compensation of temperature, for example, for resistors in electronic circuits by utilizing the response of electrical resistance of the oxide film to the rapid change of temperature.

Further, by utilizing the high response to the change of temperature, it can be used in place of bimetals of automatic chokes for automobiles, for temperature regulation of rocket engines or other engines.

In addition to the above, by utilizing the anticorrosive property, acid-resistant vessels, containers, machine parts and accessories can be produced.

The method of the invention will be explained in further detail in the following in accordance with some examples and a drawing in which the electrical charactersitics of the titanium plate with the compound oxide of the invention, are shown.

EXAMPLE Alternating current electrolysis was carried out with using metallic titanium plate as one electrode and a graphite plate as another electrode. The conditions for the electrolysis were as follows:

Electrolytic bath (aq. sulfuric acid soln.) .wt. percent 15 Frequency of power sources cycles 50 Current density ma./cm. 75 Time of electrolysis hours 2 The titanium plate which was treated with the above preliminary electrolysis, was further treated with electrolysis in an aqueous barium hydroxide solution by changing the current densities step by step as follows:

On to the titanium plate treated with the above described electrolysis, silver electrodes of 5.5 mm. in diameter where attached. Then, the relations between the changes of temperature and electric capacitance and electric resistance were measured by a bridge circuit, the results of which are shown in the attached drawing.

As will be understood from the drawing, with regard to the titanium plate having the titanium-alkaline earth metal compound oxide coating in accordance with the invention, in case that the temperature is changed rapidly which is indicated with black dots and solid lines (0-.) the electric capacitance increases and the electric resistance decreases, meanwhile, when the temperature change is stopped, and both values approach gradually against the original values with the lapse of time. On the other hand, in case that the temperature is changed gradually, which is indicated with white dots and dash lines (OO) the electric capacitance and the electric resistance change hardly.

What is claimed is:

1. A method for electrochemically forming a coating of titanium-alkaline earth metal compound oxide on the surface of titanium used as one of the electrodes in an electrolysis, which comprises carrying out an electrolytic reaction employing titanium metal for only one of the electrodes and an aqueous solution consisting essentially of an alkaline earth metal hydroxide or salt thereof as the electrolyte, and employing an alternating current power source, wherein the electrolysis is carried out for 30 minutes to 2 hours under a current density of 50 to ma./cm. then for 30 minutes to 2 hours under a current density of 75 to ma./crn. and then for 1 hour to 3 hours under a current density of 100 to ma./cm.

2. A method for forming a coating of titanium-alkaline earth metal compound oxide on the surface of titanium as claimed in claim 1, in which the titanium article to be treated is before hand treated through a preliminary electrolysis in a bath of dilute sulfuric acid and employing alternating current power source.

3. A method in accordance with claim 1 wherein one electrode employed in the electrolytic reaction is a platinum or graphite electrode.

4. A method in accordance with claim 1 wherein the electrolyte is an aqueous solution of barium hydroxide.

References Cited UNITED STATES PATENTS 3,554,881 1/1971 Piontelli 20456 R 3,551,306 12/1970 Grosso et al 20456 R R. L. ANDREWS, Assistant Examiner JOHN H. MACK, Primary Examiner 

